Abstract: A method and system for restricting telephone access to a predetermined set of telephone numbers. The method includes comparing the output of a caller ID signal decoder to telephone numbers stored in memory and allowing the telephone call to be completed if there is match between the calling party's number and a number stored in memory. The system consists of connection circuitry to which is connected a caller ID decoder, a number comparator, and an off hook detector. These components interact to restricts calls to only those stored in the number comparator.

Abstract: A framer circuit which may be implemented as a single chip is disclosed. The framer circuit performs a number of functions in a DTDM network including generating trains of empty DTDM frames, enabling the writing of data packets into specific DTDM frames and the examination of header data in specific DTDM frames to generate signals for the control of peripheral circuits. The framer circuit comprises an input serial/parallel converter, a frame detection circuit, an output parallel/serial converter and a control unit comprising one or more finite state machines for generating proper control signals such as read and write strobes for data insertion and extraction.

Abstract: An overvoltage protection circuit for communications systems for protecting equipment from power crosses on electric utility lines. A timed latch circuit is used to activate a plurality of steering SCR's which crowbar the overvoltage. The utilization of a latch circuit to activate the steering arrangement, instead of the conventional technique of using actual overvoltage line current, allows smaller devices to be used, thus reducing both circuit size and circuit power dissipation.

Abstract: An amplifier stage is disclosed having junction capacitors for by-passing high frequency signals without introducing substantial signal nonlinearities. A pair of similar serially connected diodes are reverse biased between the amplifier supply potentials. The mid-point connection of the diodes is connected to the amplifier node to be by-passed paralleling the junction capacitances of the diodes with respect to a-c potential excursions. Typical diode capacitance variations resulting from changes in the reverse bias potential across a pn junction is minimized by this arrangement.

Abstract: A folded-cascode amplifier conventionally comprises an "input" transistor of a first conductivity type receiving input signals at its base electrode, an "output" transistor of a second conductivity type, complementary to the first, connected in common-base amplifier configuration with its base electrode connected to receive fixed bias potential, and a current source supplying the combined "input" transistor collector current and "output" transistor emitter current to an interconnection between the "input" transistor collector electrode and "output" transistor emitter electrode. In the folded-cascode amplifiers herein disclosed the base electrode of the "output" transistor has the input-signal-responsive emitter potential of the "input" transistor applied to it.

Abstract: The transient photo-currents generated in the collector-base junction of an amplifier transistor responsive to transient ionizing radiation are counteracted by those similarly generated in an auxiliary p-n semiconductor junction in inverse-parallel connection with the emitter base junction of the amplifier transistor. To provide more perfect counteraction of these photo-currents, this auxiliary semiconductor junction, operated in reverse-bias, is matched in characteristics with the collector-base junction of the amplifier transistor, and the base-to-collector potential of the amplifier transistor is arranged to be substantially the same as the reverse-bias potential across the auxiliary semiconductor junction.

Abstract: An amplifier transistor has its base-to-collector voltage maintained substantially zero, and its collector-base junction has in inverse-parallel connection therewith an auxiliary semiconductor junction exposed to the same transient ionizing radiation environment. Photo-currents generated in the collector-base junction of the amplifier transistor responsive to transient ionizing radiation are counteracted by the photo-currents concurrently generated in the auxiliary semiconductor junction, so amplification can continue without being unduly hampered by such radiation.

Abstract: Each half of a differential-input amplifier stage has an input terminal connected to the emitter electrode of a transistor. Resistances are provided for sensing the flow of current through the principal conduction path of each transistor. Output signal current for the stage is taken from the collector of at least one of the transistors and applied to the input of a following one of a cascade connection of amplifier stages. Voltage comparator means sense the drop in potential across one of the resistances caused by reduction of current in one half of the diffferential-input amplifier to increase the current available to the other half. This increases the output signal current available to charge or to discharge capacitance in the stage(s) cascaded after the diffferential-input amplifier, increasing the slew rate of the cascade.